Ethylene glycol may be prepared by the liquid phase hydrogenation of glycolic acid or esterified glycolic acid in the presence of a suitable hydrogenation catalyst as described, for example, in U.S. Pat. Nos. 2,285,448; 2,607,805; and British Pat. No. 575,380. The glycolic acid is typically prepared by the sulfuric acid catalyzed carbonylation of formaldehyde as described, for example, in U.S. Pat. Nos. 2,152,852 and 2,443,482.
The crude glycolic acid obtained by the sulfuric acid catalyzed carbonylation of formaldehyde typically contains about 1.0 to 3.0 mole percent of sulfuric acid based on the moles of glycolic acid produced. It has been found that catalytic hydrogenation of glycolic acid containing sulfate in amounts typically present from the sulfuric acid catalyzed carbonylation of formaldehyde produces considerably lower yields of ethylene glycol compared with substantially sulfate-free glycolic acid. For example, when a substantially sulfate-free (less than about 0.05 weight percent sulfate) 20 percent aqueous glycolic acid solution was hydrogenated over a reduced cobalt carbonate catalyst at a temperature of 228.degree. C. and pressure of between 3600 to 4100 psig, a 94 percent yield of ethylene glycol was obtained. Under the same conditions using glycolic acid containing 1.9 mole percent sulfate, an ethylene glycol yield of only 74 percent was obtained.
Heretofore, sulfate has typically been removed from glycolic acid prepared by the sulfuric acid catalyzed carbonylation of formaldehyde by neutralization with calcium carbonate or calcium hydroxide to form insoluble calcium sulfate. Calcium sulfate, however, is a very finely divided material, is not readily settleable, and is not readily removed from the relatively viscous glycolic acid by, for example, filtration without using a filter aid such as diatomaceous earth or the like which adds to the sludge disposal problem.